Prior devices such as keyed or combination locks have been used satisfactorily for a long time to control access to an area or thing. Such devices, however, can be defeated by the use of brute force, for example, by using a hacksaw. A common method for providing more sophisticated access control consists of using an alpha and/or numeric password which is entered into the security device and compared to a pre-established code in the memory of the security device. In the case of a computer, the password is entered by the user, usually by a keyboard. The order in which the alphanumeric characters of the password are entered is part of the password. The password can be thought of as a one-dimensional matrix or a vector. In practice, because of the difficulty in remembering a random string of characters, users often use easily remembered strings, like their names or birthdays. This system can be attacked by people who can guess the password or who program another computer to try dictionary words and randomly generated passwords until a match is found. If the password consists of five characters, a randomly generated group of characters has one chance in about 45 million of matching the password. With a modern personal computer this can be accomplished in only a few minutes. If the password is made up of ten alphanumeric characters, the chance of a random match decreases to one in 1.8.times.10.sup.12. This is also within the capabilities of an inexpensive computer. Of course the security can be further increased by using a greater number of characters, but at some point (usually about 7 characters), the ability of the user's mind to memorize and retain the password is reduced to the point where the person must write down the password, thus greatly increasing the likelihood of a compromise of the security. This is especially true if the password is changed often.
While it is well known that pattern comparison can be accomplished by devices such as optical character readers, such devices rely on "reading" a finite number of points on each character and comparing that "read" against a library of the same points which will identify a character. Only a part of the pattern is matched against the library. In most cases, such approximation is sufficiently accurate for the purposes desired.
Likewise, security devices which "read" fingerprints or other physical characteristics of an individual and compare the fingerprint or other characteristic against a stored library of such data compares only a few selected points of the pattern and does not match the entire pattern. In these systems a perfect match of the pattern is not required; some predetermined percentage of the points is all that is required for a match. These devices, therefore, do not uniquely identify an individual.
Devices such as punched cards with predetermined patterns accomplish much of the same end. In a punched card, however, each element of the pattern can be in only one of two states. In the present invention there is no limit to the number of states that each element can represent. Furthermore, a punched card must be in the possession of the user and may be lost, stolen, or damaged. Other devices such as calculator keyboards may also be employed to generate a password pattern but these devices are also limited by each element of the pattern being limited to one of two possible states.